Making SMI-beamforming insensitive to the sampling timing for GSM signals

Beamforming with the sample matrix inversion method (SMI), using an antenna array, is considered for a GSM-signal. The problem of generating the reference signal from the training sequence is addressed. As the proper reference signal to be used varies with the sampling timing within the symbol interval, a modified SMI method is proposed that uses a "variable" reference signal. When working with a short training sequence, as in GSM, the performance of the standard SMI beamforming method is shown to degrade when there is an offset from the sampling instant that the reference signal was designed for. The proposed modified SMI method, however, is shown to be more or less insensitive to where in the symbol interval the sampling takes place. The proposed method achieves a better mean performance, averaged uniformly over one symbol interval.